Indexing system for color television



United States Patent O iti )INDEXENG SYSTEM FR CL TELEVESEN Wilson P. loothroyrl, Huntingdon Valley, ila., assigner,

by mesne assignments, to Philco Corporation, Philadelphia, lia., a corporation of Eeiaware Filed Nov. 23, i959, Ser. No. 854,7?1 lt- Clairns. (El. l7$-5.4)

The present invention relates to electrical systems and more particularly to cathode ray tube systems comprising a beam-intercepting structure and indexing means arranged in cooperative relationship therewith which produces signals representative of the position of the beam as it scans said structure.

The invention is particularly useful in connection with color television image presentation systems and it is in connection therewith that it will be described. lt is especially valuable in systems employing a cathode ray tube in which a single electron beam is produced and in which there is a beam-intercepting structure comprising imageforming and beam-indexing portions. The image-forming portion is composed of a plurality of sets of strips of tluorescent materials which are interspersed with one another in a selected order. Each set of strips is made from a material which emits light of a different selected color in response to the scanning `of the electron beam thereupon. To produce a colored image the scanning beam is modulated in intensity as it scans the image-forming portion by a signal representative of the color components of a scene being televised.

To insure Ithat the lmodulation of the beam is coordinated with the scanning position of the latter so that when the beam impinges upon a particular phosphor strip, say a strip emissive of red, it will he modulated by a signal whose intensity corresponds to the red content of the element then being scanned, Ithe beam-intercepting structure also has a beam-indexing portion which may consist, for example, of a plurality of parallel indexing strips arranged in a predetermined geometrical relation to selected ones of the image-forming phosphor strips. The indexing strips are made `of `a material which has a response which is detectably different from the response of other parts of the beam-intercepting structure. They may be composed, for example, of a material which has a secondary-electronemissivity which differs from the secondary-electron-emissivity of the other portions of the beam-intercepting structure. Alternatively, they may be made of Ia material which emits radiation in a portion of the electromagnetic wave spectrum which is different from the portions thereof occupied by the light emitted by the phosphor strips so as to yassist in isolating the indexing radiation from the image radiation.

lt has previously been observed that if there is only one indexing strip for each triplet or group of three adjacent phosphor strips, the phase of the fundamental component of the indexing signal generated by the scanning of the single beam thereupon is very susceptible not only to phase variations introduced by variations in the speed at which the beam is scanned, but also to variations in the intensity `of the beam when its scans the phosphor strips intermediate the indexing strips. This latter cause of phase variation seriously impairs the effectiveness of the indexing signal in establishing the desired coordination between beam intensity and position. Previously it was known that these phase errors due to the variations in beam intensity could be reduced by deriving `an indexing signal having a frequency greater than the rate at which the triplets (i.e., vgroups of three adjacent phosphor strips) are scanned. This indexing signal could be derived either by placing more than one indexing strip per triplet, or by providing one indexing strip per triplet and deriving a higher Sylhhii Fatented Nov. 5, 1953 ice harmonic of the signal produced when the beam scans the indexing strips.

While the use of higher index frequency did assist in minimizing appreciable variations in phase due to variations in the intensity of the beam as it scanned the beamintercepting structure, the higher yfrequency indexing signal contained no readily recognizable information which denoted the absolute phase position of the generated indexing signal with respect to the scanning by the beam of phosphor strips emissive of a particular color. It has hitherto been proposed to eliminate this ambiguity by providing a set of auxiliary indexing elements in addition to the usual indexing elements. The auxiliary elements produced an auxiliary indexing signal, when irnpinged upon by the beam during 1an interval when no image was being produced, which provided absolute phase information Ito lock-in the oscillator (hereinafter termed the writing oscillator) which controlled the modulation o-f the beam to correspond with its position on the screen. When the beam reproduced the image, however, a primary indexing signal was generated by the scanning of the beam over the primary indexing elements which was used to synchronize the writing oscillator.

In one arrangement of' this prior system the auxiliary indexing signal was derived from the scanning of relatively widely spaced auxiliary indexing strips located in a marginal portion of the :beam-intercepting structure, whereas the prim-ary indexing signal was derived by scanning of a number of closely spaced indexing strips positioned opposite Ithe image-forming portion of the beamintercepting structure. Since the primary indexing signal had a much higher frequency than the auxiliary indexing signal it was hitherto necessary -to provide one amplifier for amplifying the primary indexing signal and another amplier for the auxiliary indexing signad. This added to the cost and complexity of such systems.

It is therefore Ian object of the present invention to provide a less expensive indexing system of the type described.

Another object of the invention is to provide a less complex indexing system of the type described.

Still another object of the invention is to provide an indexing system of the type described which requires only an amplifier tuned to a single frequency.

ln accordance with the invention the foregoing objects are achieved in a cathode ray system of the above described type in which auxiliary indexing elements are utilized, by providing that the indexing signals derived from scanning both the auxiliary and primary indexing elements have the same given frequency thereby permitting the use of a single amplifier constructed to amplify only said iven frequency for amplifying both indexing signals. I accomplish this by modulating the beam of the cathode ray tube, when it scans the auxiliary indexing strips, by a selected signal which interacts with the signal produced by scanning of the auxiliary strips to produce an auxiliary indexing signal whose frequency is such that it can be amplified by the single amplifier. The auxiliary signal, after ampliiication in the indexing amplifier, is then mixed with the modulating signal thereby to produce a difference frequency at the frequency (hereinafter termed the writing frequency) at which the single beam is to be modulated by color-representative signals when the beam scans the image-forming portion of the screen. This difference signal will have a phase which is determined by the scanning of the auxiliary indexing strips and is used as a first synchronizing signal, during an interval in which pictorial intelligence is not being reproduced, to lock the phase' of the writing oscillator so that its output signal, at the beginning of each line, has an absolute phase determined by the scanning of the auxiliary strips.

When the beam starts to scan the image-forming portion of the screen opposite which the prhnary indexing elements are disposed, means are provided for cutting ott the modulating signal whereupon the difference signal is not produced. The primary indexing elements are so disposed that when scanned by the beam a primary indexing signal having the frequency passed by the single amplifier is produced which then is processed to produce a second synchronizing signal at the writing frequency. The second signal is used, during the scanning of the image-forming portion, to control the phase of the writing Oscillator output signal (whose initial phase was established absolutely by the auxiliary indexing signal) so that when the beam impinges on a strip emissive of a particular color it will contemporaneously be modulated by a signal representative of that color. he manner in which this is accomplished will be described in detail below.

In a preferred embodiment of the invention there is provided a single indexing amplifier which is constructed to pass a signal having a frequency m Efw where m and n are integers higher than l,

is greater than unity and fw is the writing frequency at which the beam is to be modulated by image-representative signals when it scans the image-forming portion of the screen. In a marginal portion of the beam-intercepting structure a set of auxiliary indexing strips are located which, if scanned by an unmodulated beam at a normal speed would produce an indexing signal having a frequency fw, i.e., the writing frequency. During the scanning or the auxiliary indexing strips just prior to the reproduction of each line of the image, the beam is modulated by an oscillatory wave having a frequency efr-ofw When the modulated beam impinges on the auxiliary indexing strips, a resultant auxiliary indexing signal is produced which has a frequency which can accordingly be amplified by the single indexing amplifier.

The amplified auxiliary indexing signal is then heterodyned with the modulating signal est and the difference signal fw is extracted which has a phase determined by the scanning of the auxiliary indexing strips and which is used to lock the phase of the writing oscillator output signal thereto. In so doing, the initial phase of the output signal of the writing oscillator is established just before each line is scanned.

The initial phase of the oscillatory signal is subsequently changed when the beam scans the primary indexing elements in reproducing the pictorial information of each line primarily because of variations in the rate at which the beam is deflected over the primary indexing elements associated with the image-forming portion of the screen structure. These phase changes are utilized to coordinate beam modulation with beam position so as to obtain faithful color reproduction.

To measure these variations in the beam scanning velocity a plurality of primary indexing strips are disposed opposite the image-forming portion of the screen being spaced relatively cios-e to one another so as to minimize variations in the phase of the primary indexing signal which arise from changes in the beam intensity. Their spacing is such that when an unmodulated beam traverses them at a normal speed, a signal is produced having a frequency the frequency or" the signal amplified by the single indexing amplifier.

When the beam scans the primary indexing strips during the picture portion, the modulating signal is cut oft and a primary indexing signal is produced. Since it is desired, during the scanning oi the picture, to control the phase of the writing oscillator by the phase of the primary indexing signal, the primary indexing signal is amplified and then is multiplied by n in a conventional multiplier which produces an output signal having a frequency mfw. Simultaneously, the output signal of the writing oscillator at the writing frequency fw is multiplied by (m-1) to produce a signal having a frequency (1n-Dfw. These two muitiplied signals, mfw and (1n-Dfw, are then heterodyned together to produce a difference signal at the writing frequency fw whose phase is used to loclt the phase of the output signal of the writing oscillator during the scanning of the image-forming portion of the screen. As the phase of the primary indexing signal changes because of variations in the beam scanning rate, the phase of the output signal of the Writing oscillator correspondingly changes so that the modulation of the beam intensity during the scanning of the image-forming portion is coordinated with the beam position.

The invention will be described in greater detail with reference to the appended drawings forming part of the specication and in which:

FIG. l is a block diagram, partly schematic, showing one form of a cathode ray tube system in accordance with the invention; and

FIG. 2 is a sectional view of a beam-intercepting structure suitable for the cathode ray tube system shown in FIG. l.

Referring to FIGURE 1, a cathode ray tube system is shown therein which comprises a cathode ray tube yl@ con-1 taining a cathode 12, a control grid 14, a beam-focussing electrode 16, and a beam-accelerating electrode ll-S consisting of a conductive coating on the inner wall of the envelope of the tube l0 to which an appropriate high positive value of voltage on the order of, for example, 3() lcv. is applied. A single beam i3 is emitted from the cathode 12 and is accelerated toward a beam-intercepting structure 26 which is shown in greater detail in FIG. 2. The beam 13 'is deflected by a conventional deiiection yoke 2h ywhich encircles the neck of the tube at the point where it joins the flared portion therof. |The yoke 20 is energized in a conventional manner by appropriate deiiection signals from the vertical and horizontal deilection circuits 24 which are themselves energized by appropriate synchronizing signals removed from the incoming signals by conventional synchronizing circuits (not shown).

in the arrangement shown in FIGS. l and 2, the beamintercepting structure 26 is formed directly on the faceplate ZS of the tube llt? although it may alternatively be formed on a suitable vliglfit-transparent substrate which is independent of, and spaced from, the faceplate 28. A plurality of sets of phosphor strips 3?, 32 and 34, which are emissive of red, greenv and blue iight respectively in response to the impingement of electrons thereupon, are arrayed on the faceplate 23 transverse to the direction in which the beam 13 is scanned. These phosphor strips are substantially rectilinear and may be spaced from one another if desired. rlhe materials and fabricating techniques used in constructing these phosphor strips are Well known and therefore further explanation thereof is deemed unnecessary.` On the rear surface of the strips 30, 32 and 34 is deposited an electron-permeable and conductive coating 36 =wihch may consist of a layer of aluminum, for example, which reflects light and therefore helps to increase the brightness of the image produced by the phosphor strips in front of it. This layer 36 also helps to prevent the common discoloration of phosphor screen structures by negative ions known as ion spot. A positive potential of about 25 kv. is applied to layer 36 from batteries as shown.

lIn the marginal (non-image-forming) portion L33 of the screen stnucture 26 shown in IFIG. 2 a plurality of auxiliary indexing strips 40 are located. dn the imageforming portion `4?. of the structure 2.6 primary indexing strips 44 are disposed. Both pluralities of indexing strips are disposed essentially parallel to the phosphor strips. These indexing strips, when scanned by the beam d3, release large numbers of secondary-electrons which are attracted toward the highly positive electrode i8 .whereupon the indexing strips and the layer 36 are duiven more positive. A conductive ring 29 encircles the rim of the faceplate 2S and the changes in the charge of the layer 36 create a displacement current in the ring Z9 which is passed through a condenser 33 thereby generating indexing signals which indicate the relative lateral `displacement of the beam *13. The indexing signals are applied to the single indexing ampliiier d which amplifies substantially only a single frequency, i.e.,

For illustrative purposes it will be assumed that m=5, n=3 and iw, the writing frequency, is 6.4 mc.

The number of auxiliary strips 4d per given unit of space measured in the direction of scanning is such that, scanned at the normal speed by an unmodulated beam, they would produce a signal having a frequency fw and a phase (p1. This signal, .it will be noted, cannot be amplified by the indexing amplifier Sti. It is therefore necessary to derive, during the scanning of strips 4t), indexing signals which can be amplilied in amplifier Sti.

Operation of Auxiliary Indexing Circuit 'It has previously been stated that it is desired to lock-in the output signal of the writing oscillator to an absolute phase determined by the scanning of auxiliary indexing strips such as the strips 4i) on the beam-intercepting structure. This is accomplished by the apparatus shown within the dashed-line rectangle Sil, i.e., the auxiliary indexing circuit. This circuit derives a signal from the scanning of the strips 4@ which can be amplified by the single indexing amplifier 5t) and from which a signal at the writing frequency may be derived whose phase can be fused to establish the absolute phase of the output signal of the locked oscillator 56 during the scanning of the pre-picture portion 3S.

In order to provide the latter phase-synchronizing signal the beam 13 is modulated during the pre-picture scanning period by a signal whose frequency is such that when it interacts with the signal produced by the scanning of the auxiliary indexing strips `40 a resultant output signal having a frequency lwithin the pass band of the indexing amplifier 59 will appear across condenser 33, namely aY signal fwuoei me.)

Oscillator 52, which may be of conventional construction, supplies a modulating signal (tf-Of@ 1 modulating signal aus produced by the beams impingement on strips 40 will combine to produce a sum signal and the signal which has a frequency 10.61 mc. which can be amplified in the indexing ampliiier 5t). The amplified sum signal at 10.61 mc. is -then mixed with the modulating signal (Expression l) from osci-llator 52 in a conventional mixer 54. In the output circuit of the latter -Will appear a difference signal at 6.4 rnc., i.e.,

[crawl-tenute@ It will thus be seen that the mixer 54 produces an output signal at the writing frequency having a phase determined by the rate of scanning of the auxiliary indexing strips 40' in the pue-picture portion `318. This signal is applied to the writing oscillator 'S6 only during the scanning of the pre-picture portion 3S to synchronize the phase of the writing oscillator 56 therewith.

It has been shown that in the period prior to the beginning of the scanning of each :line the writing oscillator 56 has been locked to the phase of the signal (Expression 2). `If there are variations in the rate of scanning of the image-forming portion 42 it is also necessary to synchronize the phase of the oscillator 56 to correspond therewith so that the colors of the image Will be faithfully reproduced. Accordingly there are disposed in portion 42. of the structure 26 the primary indexing strips 44 which are spaced much closer to one another than are the strips `40 in the marginal portion 33. There are as many strips 44 as there are strips 40 within a given -uni-t of space as measured in the direction of scanning. lf the elements 44 were scanned by an unmodulated electron beam at its normal scanning speed a signal would be produced across resistor 31. However, to lock the oscillator 56 during the scanning of the picture portion 4Z there must be supplied to the writing oscillator 55 a second indexing signal at the writing frequency fw (6.4 mo).

Operation of Primary Indexing Circuit put signal to oscillator 56. When the beam scans the strips 44 a primary indexing signal is produced which is applied to the amplifier 56 via the coupling capacitor 33. It should be noted that this signal may be considered as having a phase which is 5/ 3 that of the phase of the signal produced by the scanning of the auxiliary indexing strips 40 and bears a constant relation to the latter, i.e. the scanning of the first and alternate primary indexing strips 44 produces signal peaks which are separated from one another by the same amount of time as the peaks produced in scanning the auxiliary strips 4th are separated from one another. Furthermore the first peak of the primary indexing signa-l is separated from the last peak of the auxiliary signal by the same amount as the peaks of the auxiliary signal are separated from one another.

The primary indexing signal is amplified in ampliiier 50 and is then applied to a frequency multiplier 60 of conventional construction where it is multiplied by a factor n thereby producing a signal (31.83 mc.) which may be expressed as At the same time the output wave fW-l-qbl of the oscillator 55 is multiplied in a conventional multiplier 62 by (1n-1) to produce a signal i.e., 25.6 mc. The 31.83 mc. and the 25.6 mc. signal are applied to a conventional mixer 64 which produces a difference signal (6.2 me.) in its output which contains phase information relating to the rate of scanning of the strips 44. This difference signal is applied to oscillator 56 only during the scanning of the image-forming portion 42 in which the primary indexing strips 44 are located, and controls the phase of 4the output signal of the latter oscillator thereby.

Beam Modulation Processing Circuit It has already been shown how the writing oscillator 56 is locked to the phase of a iirst synchronizing signal having the writing frequency fw and a phase determined by the scanning of the auxiliary strips 40 during the prepicture portion 38, and is locked to the phase of a second synchronizing signal at the writing frequency f w during the scanning of the indexing strips 44 during the picture portion 42. The second synchronizing signal adjusts the phase of the oscillator 56 to accord with its instantaneous position measured in a horizontal direction so that modulation of the beam by image signals representative of colors emitted by the phosphor strips then being scanned is effected.

lFIG. 1 discloses one of several Iways in which this coordination may be accomplished. Apparatus is shown in the dash-line rectangle 95 for producing a signal at the writing frequency fw, which modulates the beam when the portion `42 is scanned. This signal has a phase which depends on the phase of the output signal of the Writing oscillator 56, and on the difference between the phase of the reference subcarrier and the instantaneous phase of the received chrominance components which comprise a phase and amplitude modulated subcarrier. To derive such a signal the output signal (Expression 6) of the multiplier 69 is mixed with the chrominance components of the incoming signal in a conventional mixer 66. ln the output of the mixer 66 a difference signal Where gbr is the phase of the incoming burst of the color subcarrier, to produce a difference signal This diiierence signal is then mixed with the output signal (Expression 8) of the mixer `66 to produce another difference signal which is at the Writing vfrequency and has a phase determined by the phase (gal) of the scanning of the primary indexing elements 44, the instantaneous phase (pc) of the color modulated subcarrier, and the phase (er) of the reference Wave. When this signal is applied to the grid 14, together with the luminance signal from the luminance channel (not shown), to modulate the beam 13, colored scenes will be reproduced with fidelity.

Many other variations of the system shown in FIG. 1 are possible. For example, if the writing frequency desired is 6.5 mc., the auxiliary indexing strips would be so arranged as to generate a signal at 3.2. me. whereas the primary indexing strips would generate a signal at 9.6 mc. when they are scanned by an unmodulated electron beam at normal speed. The single indexing amplifier would be tuned to 9.6 mc. and when the beam scanned the auxiliary indexing strips it would be modulated by an oscillatory wave having a frequency of 6.4 mc. As a result of the interaction of this modulating signal and the signal generated by the Iscanning of the auxiliary indexing strips, a sum signal at 9.6 me. (i.e., 6.4-$3.2 me.) is produced which is ampliiied by the single indexing amplier and mixed with the beam modulating wave at 6.4 to produce a difference signal at 3.2 mc. This difference signal is then doubled in frequency to produce `a signal at 6.4 mc. which is used to control the writing Oscillator during the pre-picture interval. In this case the writing oscillator may be the same as the oscillator which modulates the beam when it scans the auxiliary indexing strips.

When the beam scanned the primary indexing strips it would not be modulated by the 6.4 mc. wave. A primary indexing signal at 9.6 mc. is produced at the input to the single amplifier which thereupon produces an amplified output signal at 9.6 me. which is mixed with the output wave of the oscillator at 6.4 mc. to produce a difference frequency ysignal at 3.2 me. This difference signal is then doubled to produce a second 6.4 mc. signal for synchronizing the phase of the writing oscillator during the scanning of 'the picture portion of the beam-intercepting structure.

Still other systems are possible which would employ the present invention, as for example, one in which the auxiliary indexing strips are so disposed as to produce a signal at 6.4 mc. when scanned by an unmodulated beam and wherein the primary indexing strips are arranged to produce a signal at 9.6 mc. The beam is modulated by a 16 mc. signal as it scans the auxiliary indexing strips and a difference signal at 9.6- mc. is derived therefrom. A single indexing amplifier tuned to 9.6 mc. amplies the auxiliary indexing signal which is then mixed with the i16 me. modulating signal to produce a rst synchronizing signal at 6.4 mc. for locking the phase of fthe Writing oscillator thereto. On the other hand, when the beam scans the primary indexing strips the beam is not modulated by the 16 me. signal and the primary indexing signal at 9.6 mc. is produced and amplified. It is then heterodyned with the 16 mc. signal to produce a second synchronizing signal at 6.4 me. yfor locking the phase of the writing oscillator output signal thereto.

In all orf these variations only one amplifier tuned 'to a single frequency is necessary to produce excellent results insofar as the proper functioning of the indexing system is concerned.

What is claimed is:

1. A cathode ray tube system comprising: a cathode ray tube having means for producing an electron beam therein, -a beam-intercepting structure comprising first and second pluralities of indexing elements, means for deflecting said beam over said intercepting structure at a predetermined velocity, said first and second plunalities of indexing elements having respectively different periodicities to produce, in response to electrons impingent thereupon, first and second signals having respective first and second nominal frequencies, a single means for amplifying only signals generated in the scanning of said elements which have said second nominal frequency, and means :for modifying said beam when it scans said first plurality of elements so that when the latter elements are scanned they generate a signal having substantially said second nominal lfrequency.

2. A cathode ray tube system according to claim l wherein said beam-modifying means includes means for modulating said beam by a modulating signal substantially only wheny said first plurality of elements are scanned, said modulating signal having a frequency such that it interacts with the signal generated by scanning said first plurality of elements to pnoduce a signal having substantially said second nominal frequency.

3. A cathode ray tube system comprising: a cathode ray tube containing means for producing an electron beam, a beam-intercepting structure comprising a first plurality of indexing elements which recur with a given periodicity, and a second plurality of indexing elements which recur at a periodicity which is a fractional multiple olf said first periodicity7 means for scanning said beam over said `structure thereby toproduce first and second indexing signals corresponding respectively to the rates at which said first and second pluralities are traversed by said beam, said second signal having :substantially a predetermined nominal frequency, means for modulating said beam by a first modulating signal substantially only as it traverses said first plurality of inexing elements whereupon said first modulating signal and said first indexing signal interact to produce a first dierence frequency signal at said nominal frequency, a single amplifying means which amplifies said first difference frequency signal and said second indexing signal, said amplifying means being constructed to amplify substantially only signals at said nominal frequency, means for producing an oscillatory Wave, means responsive to said first modulating signal and to said amplified first difference frequency signal for applying a first synchronizing signal to said loscillating .sans during the scanning of said first plurality of indexing elements thereby to control the frequency of said oscillatory wave, means -for multiplying the frequency of said amplified second indexing signal to produce a first product frequency signal, means for multiplying the frequency of said 'oscillatory Wave to pnoduce a second product frequency signal, and means responsive to said first and second product frequency signals r For supplying to said -oscillating means Ia second synchronizing signal having the same frequency as said first synchronizing `signal substantially only when said beam scans said second plurality of indexing elements.

4. A cathode ray tube system comprising: a cathode ray tube containing means for producing an electron beam therein, a beam-intercepting structure comprising a plurality of image-forming elements and a beam-indexing portion in a predetermined spatial relation thereto, said indexing portion including an auxiliary indexing portion containing a relatively low number of auxiliary indexing elements per unit of space measured in a direction transverse to the axes of said elements, said indexing portion also including a pirmary indexing portion containing times as many primary indexing elements as said auxiliary portion contains per said unit of space, where m and n are integers greater than l and ITL is greater than l, means for deflecting said beam over said auxiliary and primary indexing portions, the impingement of said beam on said primary portion causing the generation of a primary indexing signal having a frequency nf Where f is a predetermined frequenecy, means for modulating said beam at a frequency when said beam is deflected over said auxiliary portion, the interaction of the modulation of said beam and the signal resulting from the impingement of said beam on said auxiliary portion producing an auxiliary indexing signal having a frequency means for ampiifying both said primary and auxiliary inexing signals, said amplifying means being constructed to amplify substantially only signals having a frequency m gf means for combining the amplified auxiliary indexing signal with a signal m (Vlif from said modulating means to produce a first synchronizing signal substantially at a frequency f, an oscillator for producing an output Wave substantially at said frequency f, means for supplying said first synchronizing signal f to synchronize said oscillator substantially only when said beam scans said auxiliary indexing portion, means for multiplying said primary indexing signal by n to produce l a signal having a frequency mf, means for multiplying the output Wave of said oscillator by (m-l) to produce a signal having a frequency (rn-lh, means for combining said signals mf and (1n-Uf to produce a second synchronizing signal having a frequency f, and means for applying said second synchronizing signal to said oscillator to synchronize the latter substantially only when said beam scans said primary indexing elements,

5. In a color image-producing system, a color imageproducing cathode ray tube having an image screen to be scanned line-by-line by an electron beam Within the tube, means for effecting the scanning motion of the electron beam, means for modulating the electron beam with a signal representative of color content of the image to be produced, two sets of indexing elements on said screen, which sets are scanned successively by said beam and have respectively different periodicities, one set of indexing elements producing an indexing signal having a predetermined nominal frequency as the elements are scanned by said beam, means for modifying said beam during its scanning of the other set of indexing elements so that the latter produce another indexing signal having the same nominal frequency as said first indexing signal, common amplifier means for amplifying both of said indexing sig- 1 l nais, and means for utilizing the amplified signals to effect proper time coordination between color signal modulation and position of said beam.

6. A color image-producing system according to claim 5, wherein an oscillator controls the color signal modulation of said beam, and the amplified indexing signals are utilized to control said oscillator.

7. A color image-producing system according to claim 5, wherein the means for modifying said beam during its scanning of the other set of indexing elements comprises an oscillator and means for turning the oscillator on during the scanning of said other set of indexing elements.

8. In a color image-producing system for a color television receiver which receives a color television signal including a chrominance component, a color image-producing cathode ray tube having an image screen to be scanned linebyline by an electron beam within the tube, means for effecting the scanning motion of the electron beam, colored light-emissive elements on said screen which successively and repetitively emit light of different colors in response to electron beam impingement during each line scan, means for effecting chrominance modulation of said beam according to said chrominance component, two sets of indexing elements on said screen, which sets are scanned successively by said beam and have respectively different periodicities, one set of indexing elements producing an indexing signal having a predetermined nominal frequency as the elements are scanned by said beam, means for modifying said beam during its scanning of the other set of indexing elements so that the latter produce another indexing signal having the same nominal frequency as said first indexing signal, common amplifier means for amplifying both of said indexing signals, and means for utilizing the amplified indexing signals to effect proper time coordination between chrominance modulation and position of said beam.

9. In a color image-producing system for a color television receiver which receives a color television signal including a chrominance component, a color image-producing cathode ray tube having an image screen to be scanned line-by-line by an electron beam within the tube, means for effecting the scanning motion of the electron beam, colored light-emissive elements on said screen which successively and repetitively emit light of different colors in response to electron beam impingernent during each line scan, means for effecting chromiuance modulation of said beam according to said chrominance component, a first set of indexing elements on a pre-image portion of said screen, a second set of indexing elements on an imageforming portion of said screen, said sets of elements having respectively different periodicities, said second set of elements producing an indexing signal having a predetermined nominal frequency as the elements are scanned by said beam, means for modifying said beam during its scanning of said first set of elements so that the latter produce another indexing signal having the same nominal frequency as said first indexing signal, common amplifier means for amplifying both of said indexing signals, and

means for utilizing the amplified indexing signals to effect proper time coordination between chrominance modulation and position of said beam.

l0. A color image-producing system according to claim 9, wherein the means for effecting chrominance modulation of said beam includes an oscillator, the indexing signal produced by beam scanning of said first set of elements is ultilized to phase said oscillator at the start of each line scan, and the indexing signal produced by beam scanning of said second set of elements is utilized to control the phase of the oscillator during each line scan of the image-forming portion of said screen.

l1. A color image-producing system according to claim 9, wherein 'a beam-modulating oscillator is provided and is turned on only during the beam scanning of said first set of elements to cause production of said other indexing signal.

l2. A color image-producing system taccording to claim 9, wherein the means for effecting chrominance modulation of said beamv includes an oscillator, said system further comprising means for producing from said other indexing signal a first signal for synchronizing said oscillator during beam scanning of said first set of elements, and means for producing from said first indexing signal a second signal for synchronizing said oscillator during beam scanning of said second set of elements.

13. In a cathode ray tube system, a cathode ray tube having means for producing an electron beam thereto, a beam-intercepting structure `comprising first and second pluralities of indexing elements having respectively different pefriodicities, means for defiecting said beam over said structure, said second plurality of indexing elements producing a signal having substantially la given frequency when scanned by said beam, means for modulating said lbeam during its scanning of said first plurality of indexing elements to produce another signal having substantially said given frequency, a single means responsive to signals substantially iat said given frequency for amplifying said two produced signals, means coupled to said `beammodulating means and to said single amplifying means for producing a third signal having a frequency different from said given frequency whenever said beam scans said rst plurality of elements, and means cooperating with said single amplifying means for producing a fourth signal at said different frequency in response to the scanning by said beam of said second pluarlity of indexing elements.

14. A cathode ray tube system according to claim 13, further including an oscillator operable at said different frequency, and means for supplying said third and fourth signals to said oscillator to synchronize the latter.

Sunstein Jan. 22, 1957 Graham et al July l2, 1960 

1. A CATHODE RAY TUBE SYSTEM COMPRISING: A CATHODE RAY TUBE HAVING MEANS FOR PRODUCING AN ELECTRON BEAM THEREIN, A BEAM-INTERCEPTING STRUCTURE COMPRISING FIRST AND SECOND PLURALITIES OF INDEXING ELEMENTS, MEANS FOR DEFLECTING SAID BEAM OVER SAID INTERCEPTING STRUCTURE AT A PREDETERMINED VELOCITY, SAID FIRST AND SECOND PLURALITIES OF INDEXING ELEMENTS HAVING RESPECTIVELY DIFFERENT PERIODICITIES TO PRODUCE, IN RESPONSE TO ELECTRONS IMPINGENT THEREUPON, FIRST AND SECOND SIGNALS HAVING RESPECTIVE FIRST AND SECOND NOMINAL FREQUENCIES, A SINGLE MEANS FOR AMPLIFYING ONLY SIGNALS GENERATED IN THE SCANNING OF SAID ELEMENTS WHICH HAVE SAID SECOND NOMINAL FREQUENCY, AND 